The conventional surface protective layer and interlayer insulating layer for a semiconductor device includes a polyimide resin that can have excellent heat resistance, electrical properties, mechanical properties, and the like, as an alkali soluble resin. The polyimide resin has recently been used as a photosensitive polyimide precursor composition which can be coated easily. The photosensitive polyimide precursor composition can be coated on a semiconductor device, patterned by ultraviolet (UV) rays, developed, and heat imidized, to easily provide a surface protective layer, an interlayer insulating layer, and the like. The use of a photosensitive polyimide precursor composition may be shorten process times as compared to a conventional non-photosensitive polyimide precursor composition.
The photosensitive polyimide precursor composition can be a positive type in which an exposed part is dissolved by development, or a negative type in which the exposed part is cured and maintained. Positive type compositions can be developed by a non-toxic alkali aqueous solution.
The positive photosensitive polyimide precursor composition can include a polyimide precursor of polyamic acid, a photosensitive material of diazonaphthoquinone, and the like. However, it can be difficult to obtain a desired pattern using the positive photosensitive polyimide precursor composition because the carboxylic acid of the polyamic acid is too highly soluble in an alkali.
In order to solve this problem, a material in which a polybenzoxazole precursor is mixed with a diazonaphthoquinone compound has drawn attention. When the polybenzoxazole precursor composition is actually used, however, film loss of an unexposed part can be significantly increased, so it can be difficult to obtain a desirable pattern after the developing process.
In order to improve this, if the molecular weight of the polybenzoxazole precursor is increased, the amount of film loss of the unexposed part can be reduced. Development residue (scum), however, can be generated, so resolution may be decreased and the development duration on the exposed part may be increased.
In order to solve this problem, film loss can be suppressed in unexposed parts during development by adding a certain phenol compound to a polybenzoxazole precursor. However, the effect of suppressing the film loss of the unexposed part is insufficient. Accordingly, there is still a need to increase the effects on suppressing the film loss, along with preventing generation of the development residue (scum). In addition, there is a need for research directed to a dissolution-suppressing agent, since phenol compounds used to adjust solubility can decompose at high temperatures during curing, can undergo a side reaction, or the like, which can damage mechanical properties of a cured film.
Furthermore, when this polyimide precursor composition or polybenzoxazole precursor composition is prepared into a thermally cured film, the thermally cured film can remain in the semiconductor device and can act as a surface protective layer, and accordingly should have excellent mechanical properties such as tensile strength, elongation, Young's modulus, and the like. However, generally-used polyimide precursors or polybenzoxazole precursors tend to have inappropriate mechanical properties, and in particular, elongation, and also can have poor heat resistance.
In order to solve this problem, various additives can be added thereto or a precursor compound that is cross-linkable during the thermal curing can be used. However, while such additives and/or precursor compounds may improve mechanical properties, and in particular elongation, they may not provide desired optical properties such as sensitivity, resolution, and the like. Accordingly, there is still a need for methods that do not deteriorate these optical properties and can be still attain excellent mechanical properties.